Tanged screw thread inserts with improved removability

ABSTRACT

A helical thread insert having a removable tang attached to the front end of the insert, a retention device and a removal notch located along the rear portion of the insert. The removable tang is oriented radially inward and includes a “V” shaped notch oriented along the bottom of the thread to detach the tang at a specified point. The retention device is located at the rear end of the thread insert and prevents counterclockwise, removal rotation of the insert by engaging the female threads of the bore which the helical thread insert is disposed. A removal notch is formed along the inner surface of the insert proximal to the retention device to allow a tool to actuate the retention device inward, away from the female threads of the parent material, to allow relatively free counterclockwise rotation, removal, of the thread insert.

FIELD OF THE INVENTION

[0001] The present invention relates to a thread insert. More specifically, the present invention relates to a helical thread insert having a removable tang for installation, a removal notch formed in the last thread of the insert and a retention device.

BACKGROUND OF THE INVENTION

[0002] Helical thread inserts are used in many industries to provide female threads in a threaded bore located in a parent material having a relatively low hardness. The helical thread inserts are installed using a special tool that grasps a removable tang located at the leading end of the helical thread insert and guides the insert into the threaded bore in the parent material. The tang is then removed to provide a threaded bore having full thread engagement and female threads with a greater hardness than the female threads formed in the original threaded bore. In the event that the helical thread inserts become worn or damaged, removal of the thread insert may be required.

[0003] In recognition of the need to remove helical thread inserts several devices have been developed. Some helical thread inserts include a pair of diametrically opposed notches formed in the last thread of the insert. The notches allow a flathead screwdriver or other tool to apply a counterclockwise torque to guide the insert out of the original threaded bore. However, the use of a flathead screwdriver or other tool may apply forces that drive the insert back into the threaded bore or expand the last thread of the insert radially outward. If the tool applies a force on the insert that pushes the insert back into the original threaded bore, removal of the thread insert is made more difficult because the desired direction of movement of the insert, out of the hole, is opposite of the force that is applied on the insert. Additionally, if the tool causes expansion of the last thread of the insert, the end of the thread may dig into the parent material causing removal of the thread insert to be more difficult and possibly damaging the parent material. In recognition, thread inserts have been developed that have chamfered and radiused edges formed around the end of the last thread to prevent the thread from digging into the parent material.

[0004] However, one concern associated with helical thread inserts is retention capability, the ability of the insert to remain in the threaded bore. The use of chamfered or radiused ends reduces the ability of the end of the thread insert to grasp the parent material to prevent counterclockwise movement, leading to inadvertent removal of the insert. Additionally, the increasing popularity of stainless steel helical thread inserts in combination with stainless steel threaded fasteners may lead to galling. If galling occurs, the forces applied to the threaded fastener are directly transferred to the helical thread insert, thus increasing the likelihood that the helical thread insert will not remain in the threaded bore.

SUMMARY OF THE INVENTION

[0005] Accordingly, the present invention provides a helical thread insert having a tang for installation, a square end providing increased retention and a removal notch. The tang attached to the front end of the helical thread insert to provide a means of installing the insert. The retention device prevents counterclockwise rotation of the insert that may lead to inadvertent removal of the insert. The removal notch providing a means of selectively removing the insert counterclockwise without engaging the retention device.

[0006] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0008]FIG. 1 is a rear view of a prior art thread insert;

[0009]FIG. 2 is a side view of the thread insert according to the preferred embodiment;

[0010]FIG. 3 is a rear view of the thread insert according to the preferred embodiment;

[0011]FIG. 4 is a front view of the thread insert according to the preferred embodiment;

[0012]FIG. 5 is a back view of the prior art thread insert of FIG. 1 disposed in a workpiece;

[0013]FIG. 6 is a back view of the thread insert of the present invention disposed in a workpiece; and

[0014]FIG. 7 is a cross sectional view taken along plane AA of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0016]FIG. 1 illustrates a prior art helical thread insert 1. Helical thread insert 1 is formed of a coiled wire body 2, having a tang 4 located at the leading end for installation and a pair of removal notches 6A and 6B located at the trailing end 7. The removal notches are positioned in a diametrically opposed orientation to allow a tool such as a flathead screwdriver to remove the insert. The trailing end 7 of the coil, includes chamfers 8 and 9 to prevent trailing end 7 from digging into the female threads of the bore which it is installed.

[0017] FIGS. 2-4 illustrate a helical thread insert 10 constructed in accordance with the preferred embodiment of the present invention. The helical thread insert 10 is generally comprised of a front end portion 12 and a rear end portion 14 interconnected by a central portion 13. The helical shape of the insert is preferably formed to provide a male thread 22 along the outer surface of helical thread insert 10 that is complementary to female threads 44 (not shown) formed in the parent material 40 (not shown) and a female thread 20 located along the inner surface of the helical thread insert 10 having substantially higher hardness than the relatively low hardness of the parent material 40.

[0018] In a preferred embodiment of the present invention, a tang 16 is attached to the front end portion 12 of the helical thread insert 10 to assist in installing the helical thread insert 10 in the threaded bore 42. Tang 16 extends radially inward from the distal end of the front end portion 12 to provide a means of grasping the helical thread insert while applying a rotational force to guide the helical thread insert 10 into the threaded bore 42. It is also desirable that helical thread insert 10 include a device to detach tang 16 from the front end portion 12 to allow a threaded fastener to extend further than the depth of the helical thread insert 10 (e.g. a through hole). In the preferred embodiment of the present invention a notch 24 is formed along the bottom of the first thread at the front end portion 12. Notch 24 is formed in a “V” shape to have a first plane 24A and a second plane 24B intersecting to form a line 24C that is the terminus of the notch.

[0019] To remove tang 16 from the front end portion 12 of the helical thread insert 10 a simple implement may be used to apply a force on tang 16. Once a requisite force has been applied, tang 16 will fracture proximal to notch 24 as a result of the increased stress concentration at notch 24.

[0020]FIG. 5 shows a prior art helical thread insert 1 disposed in a threaded bore 42 of a parent material 40. Once the helical thread insert 10 has been installed in the parent material 40 it is desirable that the helical thread insert 10 remain installed in the threaded bore 42. However, external forces may apply counterclockwise torques on the helical thread insert 10 that may rotate the helical thread insert 10 in a counterclockwise direction, possibly causing helical thread insert 10 to be inadvertently removed from the threaded bore 42. Conditions such as galling and vibrations also increase the effect of forces that act on the helical thread insert 10. As shown, end 7, is positioned adjacent to the female threads 44 of the parent material 40. Chamfers 8 and 9 provide a ramped face by which the female threads 44 can pass with little resistance possible leading to inadvertent removal.

[0021]FIG. 6 shows helical thread insert 10 disposed in a threaded bore 42 located within parent material 40. In the preferred embodiment of the present invention provides a retention device, face 32, located at the terminating end of the rear end portion 14 prevents counterclockwise rotation of the thread insert. Male thread 22, and more specifically, edge 34 of face 32 is located adjacent to female threads 44 of the threaded bore 42. In the event that a counterclockwise, removing, torque is applied to the helical thread insert 10, edge 34 begins to move along the female threads 44 and digs into the parent material 40 due to the normal orientation of face 32 and the difference in the hardness of the helical thread insert 10 and the parent material 40. Edge 34 effectively prevents counterclockwise rotation of the helical thread insert 10 by transferring the forces that act on helical thread insert 10 to the parent material 40.

[0022] In situations where helical thread inserts are worn, damaged or unwanted, it may be necessary to remove them from the threaded bore 42 without damaging the female threads 44. The helical thread insert 10 of the present invention provides a device, removal notch 18 to aid in removal of the helical thread insert 10. Removal notch 18 is formed in the last female thread of rear end portion 14. Removal notch 18 is comprised of a engagement face 50 that extends generally inward from female threads 20 at an acute angle, an outer face 52 that is substantially parallel to the longitudinal direction of helical thread insert 10 and a relief face 54 that forms the end portion of removal notch 18.

[0023] As shown in FIG. 7, removal notch 18 provides a means of engaging helical thread insert 10 and applying a counterclockwise torque for removal of the helical thread insert 10. Additionally, removal notch 18 of the present invention allows a tool to direct face 32 and more importantly edge 34 inward to the direction of arrow A, eliminating the contact of edge 34 with female threads 44 thereby preventing digging into the relatively low hardness parent material.

[0024] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

What is claimed is:
 1. A helical thread insert comprising; a front end portion having a removable tang attached thereto; a central portion formed of coiled wire defining male threads along an outer surface and female threads along an inner surface; and a rear portion having an end surface formed perpendicular to the longitudinal direction of the coil and a notch formed along the inner surface and proximal to the end surface.
 2. The helical thread insert of claim 1, wherein the front end portion further comprises a “V”-shaped notch defining a separation point between the removable tang and the front end portion.
 3. The helical thread insert of claim 1, wherein the end surface is completely flat.
 4. The helical thread insert of claim 1, wherein the notch is further comprised of an engaging surface, an outer surface and a relief surface.
 5. The helical thread insert of claim 4, wherein said engaging surface extends generally inward from the female threads along the inner surface at an acute angle.
 6. The helical thread insert of claim 5, wherein said outer surface extends along a line defining a boundary between the female threads and the male threads.
 7. The helical thread insert of claim 6, wherein said relief surface defines the rear portion of the notch and is substantially parallel to the engaging surface.
 8. A thread insert formed of coiled wire defining male threads along an outer surface and female threads along an inner surface, the insert comprising; a notch formed in a female thread located near a first end of the thread insert, a flat surface formed at the end of the thread insert for operatively retaining the insert in a threaded bore. 